Phytochemical-mediated differential acceptance of four rutaceous plants by a swallowtail butterfly, Papilio polytes (Lepidoptera: Papilionidae).

Abstract

Papilio polytes, a Rutaceae feeder, exploits only a few plant species as larval food plants in nature. To clarify the physiochemical factors underlying its narrow host range, we examined the acceptability of four rutaceous plants, Citrus depressa (a host plant) and other potential hosts, Fagara ailanthoides, Evodia meliifolia, and Orixa japonica, to ovipositing females of the butterfly. Female responses to the foliage, methanol extracts and partitioned fractions prepared from these plants were assayed for the presence of oviposition stimulants and/or deterrents. The foliage and methanol extracts of C. depressa and F. ailanthoides readily induced egg-laying, while those of E. meliifolia evoked weak responses from females. In contrast, ovipositing females never accepted O. japonica. Further experiments with fractions derived from the respective plants revealed that C. depressa and F. ailanthoides contained potent oviposition stimulant(s) and E. meliifolia, both moderate stimulant(s) and weak deterrent(s). Negative oviposition response to O. japonica proved to be ascribed to the presence of weak deterrent(s) and the lack of any appreciable stimulant(s). Larval survivorship on these plants was also recorded as an estimate of fitness. In good coincidence with female oviposition responses, both 1st- and 5th-stadium larvae performed well on C. depressa and F. ailanthoides, while larval performance appeared a little worse on E. meliifolia. On the other hand, the survivorships of two larval stadia on O. japonica differed greatly from each other: whereas the mortality of neonates was very high, 5th stadium larvae grew into pupae as well or better on this plant as compared to E. meliifolia. These results suggest that the four rutaceous plants are arrayed as follows in decreasing order of acceptability: C. depressa5F. ailanthoides.E. meliifolia. .O. japonica.